Inflection PointThe point on the Frequency vs. Temperature curve where the
change in frequency changes from positive to negative. In the case
of a AT-Cut fundamental mode crystal, the Inflection Point is
located between 25 - 35 degrees Celsius dependent on the cut angle
and mechanical construction of the device. In theory, a crystal
whose cut angle is 35 degrees 13 minutes will have an Inflection
Point located at 25 degrees C. or room temperature. This reference
angle is called the Theta Angle and engineers design with curves
identify as plus or minus from the Theta Angle". The curve can
identify a specific angle to produce a specific Frequency vs.
Temperature characteristic.